1. Field of the Invention
The present invention relates to an imaging lens and an imaging apparatus, more particularly, to an imaging lens suitable to be used in a surveillance camera, a camera for portable terminal, an on-board camera, and the like employing an imaging device such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor), and an imaging apparatus having the imaging lens.
2. Description of Related Art
Recently, imaging devices such as CCD and CMOS have been to a great extent miniaturized and the number of pixels thereof excessively increased. In addition, an imaging apparatus main body having the imaging device has also been miniaturized, and thus it is also required not only to achieve favorable optical performance but also to achieve weight reduction and miniaturization of an imaging lens mounted therein.
On the other hand, it is required for on-board cameras, surveillance cameras, and the like to have, for example, a wide angle lens, of which a total angle of view is larger than 130 degrees, with high antiweatherability, a small size, and high performance.
In this field, known imaging lenses having a small number of lenses include, for example, the lens systems disclosed in JP-A-2002-244031, JP-A-2006-259704 and JP-A-2007-133324. JP-A-2002-244031 and JP-A-2006-259704 disclose an imaging lens configured to include four elements. JP-A-2007-133324 discloses a lens unit formed of an imaging lens configured to include three elements and a glass protective plate disposed on the object side thereof.
In the imaging lenses used in the imaging apparatuses in the above-mentioned field, the first lens disposed closest to the object side may be made of glass in order to increase antiweatherability. Generally, the diameter of the first lens is larger than those of other lenses. In particular, in wide angle lenses, heights of rays incident on the first lens are large. Hence, the diameter of the first lens is essentially large.
However, if the first lens with a large diameter is made of glass, costs thereof increase. In the imaging lenses in the above-mentioned field, not only the demands for miniaturization, high performance, and an increase in angle of view but also the demand for low cost has become stronger. Recently, the demands have become stronger and stronger. In order to achieve low cost, it is of great importance, for example, to increase an allowance for manufacturing errors.
In the lens systems disclosed in JP-A-2002-244031 and JP-A-2006-259704, the power of the first lens is strong. Hence, it is difficult to stabilize performance reliably when increasing the allowances for manufacturing errors. As a result, it is difficult to achieve low cost.
In the lens unit disclosed in JP-A-2007-133324, it is possible to expect improvement in antiweatherability by employing a protective plate. However, this configuration is insufficient for an increase in angle of view of the imaging lens itself.